This invention relates to solid fuel pulverizing and firing systems for fossil fuel furnaces of the type, wherein the fossil fuel furnace and a substantial portion of the solid fuel pulverizing and firing system by means of which solid fuel and air is supplied to the fossil fuel furnace, are operated at a predetermined pressure, and more specifically, to an exhauster employable in such solid fuel pulverizing and firing systems for fossil fuel furnaces having an improved fan assembly.
Three basic types of solid fuel pulverizer firing systems find common use. These are the direct-fired system, the semi-direct fired system, and the bin storage system. The simplest and most commonly used of these three systems, and the one to which the present invention is directed, is the direct-fired system in which solid fuel, e.g., coal, is fed in a suitable manner along with hot gases to a pulverizer. The solid fuel is simultaneously ground and dried within the pulverizer as the gases sweep through the pulverizer. The gases are cooled and humidified by means of the evaporation of the moisture contained in the solid fuel. Often, an exhauster is employed for purposes of removing the hot gases and the entrained fine solid fuel particles, i.e., the solid fuel that has been ground within the pulverizer, from the pulverizer. Moreover, this exhauster, when so employed, is located on the discharge side of the pulverizer and is operative to effect the delivery of the mixture of hot gases and entrained fine solid fuel particles to a fossil fuel furnace. The main advantages of the direct-fired system are simplicity, low cost and maximum safety. To this end, the fine solid particles, which can be subject to spontaneous combustion and thus are considered to be potentially hazardous, go directly to the fossil fuel furnace at high velocities, and thus are not given the opportunity to collect and possibly ignite spontaneously. Accordingly, the direct-fired system can be operated at the maximum temperatures that safety will permit.
One prior art form of such a direct-fired solid fuel pulverizer firing system is depicted in U.S. Pat. No. 3,205,843 entitled “Pulverized Coal Firing System” which is incorporated herewithin by reference in which it is disclosed that solid fuel passes through the inlet chute of the pulverizer onto a rotating bowl thereof. The solid fuel is pulverized by the grinding rollers of the pulverizer, which are mounted within the pulverizer housing to provide a grinding action between the grinding rollers and a grinding ring provided on the rotating bowl of the pulverizer. Air passes up through the pulverizer between the housing thereof and the rim of the rotating bowl whereby pulverized solid fuel is entrained in this air with the air-pulverized solid fuel mixture passing up into a classifier. The classifier separates the coarse solid fuel fractions and returns these fractions to the rotating bowl of the pulverizer for regrinding, while the fines retained in the air stream pass through the outlet of the pulverizer. From this outlet of the pulverizer, the air-pulverized solid fuel mixture is conveyed to the inlet of the exhauster via a conduit. The air-pulverized solid fuel mixture in turn is conveyed from the exhauster to a fossil fuel furnace through ducts.
Another prior art form of an exhauster for a solid fuel pulverizer firing system is depicted in U.S. Pat. No. 5,363,776 to Wark entitled “Exhauster Inlet Venturi” which is incorporated herewithin by reference. The Wark '776 patent discloses a known pulverizer exhauster fan assembly having a fan with a plurality of radial fan blades connected to a drive shaft by a spider assembly. The drive shaft ends in a hub, which is capped by a radial diverter cap.
Although solid fuel pulverizer firing systems constructed in accordance with the teachings of the two referenced issued U.S. patents have been demonstrated to be operative for the purpose for which they have been designed, presently large efficiency losses occur when pulverized coal enters a furnace by passing though the center of an exhauster fan. Furthermore, the impact between the paddles of the fan and the coal particles wears away at the fan components. Therefore, a need exists for a device or system capable of improving the efficiency of the exhauster assembly and reduces the wear and maintenance of the exhauster assembly.
According to an aspect illustrated herein, an exhauster bypass system includes a housing having an inlet for receiving an input flow including a gas and particle mixture. The housing further includes a central outlet for providing a central output flow including a particle deficient gas stream to an exhauster, and a bypass outlet for providing a bypass flow including a particle-laden gas stream to the exhauster. A louver separates at least a portion of the particles of the input flow from the central flow to the bypass flow. The central flow is provided to a fan of the exhauster and the bypass flow is provided to the exhauster away from the fan.
According to another aspect illustrated herein, a method of providing a central flow and a bypass flow to an exhauster assembly includes separating at least a portion of an input flow including a gas and particle mixture into a central output flow including a particle deficient gas stream, and a bypass flow including a particle-laden gas stream. The central flow is provided to a fan of the exhauster assembly. The bypass flow is provided to the exhauster assembly away from the fan.
According to another aspect illustrated herein, an exhauster bypass system includes means for receiving an input flow including a gas and particle mixture, and means for separating at least a portion of the particles of the input flow from a central flow, wherein the separated particles are provide to a bypass flow. The exhauster bypass system further includes means for providing the central output flow including a particle deficient gas stream to a fan of an exhauster, and means for providing a bypass flow including a particle-laden gas stream to the exhauster away from the fan.